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The Monitored Man

For years, health advocates have been telling us to move more. But just how much more?

A multitude of activity tracking devices now promise to answer that question. Generally, these digital monitors, which can be worn around the wrist, on collars and belts, even as jewelry, record how and how much you move throughout the day. Some aim to do a great deal more. Makers of the devices have begun intensive campaigns aimed at convincing the large population of “worried well” consumers to get wired and start recording their every move.

Wired Well

High-tech fitness and activity trackers all share one thing: an accelerometer. Here’s how they work — and don’t.

How well do these work? Curious about the benefits and limits, I’ve been testing as many different models as possible — wearing them day and night for six months, 11 models in all, sometimes four at once. I’ve learned a great deal about these gadgets. And about myself.

I’d thought I was a fairly active person: I bike to work most days and hit the gym or get other physical activity two or three times a week. The trackers, on the other hand, showed that aside from those spates of exercise, for the vast majority of each day I was completely sedentary.

But that may not be the whole story.

Activity trackers typically combine a wearable device with a website or smartphone app to view data collected about your movements. The goal is to measure not only your steps from the parking lot to your desk, but also your sedentary down time at work or in front of a television, bursts of intense exercise and even your sleep habits — all to create a complete picture of your most and least healthful behaviors. Some models also offer tips and set goals based on your data.

The most popular models are made by Fitbit, Nike and Jawbone; the gadgets typically cost $60 to $200. Most are made of rubber and plastic and come in a choice of colors, with the notable exception of the Shine, made of metal by Misfit Wearables.

In 2013, activity trackers generated an estimated $290 million in American retail sales, according to Ben Arnold, an analyst at New York’s NPD Group, who says the market could double this year. The sharp rise of trackers stems from advances in chip technology. The devices all share a common sensor, an accelerometer that can track movement in three dimensions (up and down, side to side, and forward and back). Accelerometers can now be made small enough and at a low enough cost that they can be embedded in almost anything.

While all activity trackers have an accelerometer, some include additional sensors to pick up other signs of activity. BodyMedia makes an armband that measures perspiration and muscle heat for a more accurate assessment of activity level and calories burned. Basis Science sells the B1 Band watch, which measures heart rate, perspiration and skin temperature. The Pulse, from Withings of France, can measure resting heart rate.

Many trackers estimate the length and fitfulness of sleep by sensing how much you move throughout the night. And Polar and Garmin both make trackers that can pair with chest straps to record heart rate during a workout.

But even the best tracker can’t recognize all of your movements. As I sit writing this, my wrists are motionless, but my leg is tapping to music. My activity trackers don’t seem to notice — fidgeting won’t be reflected in the calorie counts they show me. That’s too bad, because there’s an interesting body of research suggesting that a propensity to fidget is one reason lean people stay lean.

More surprisingly, perhaps, only the trackers made by Basis and BodyMedia gave me credit for being active when riding my bike. Most of the rest just sat on my wrist, recording no activity — and true enough, my wrist wasn’t moving much as I pedaled through the city traffic. All of them were more accurate when I was playing tennis.

Activity trackers usually don’t measure exertion, only motion. Company officials say that intense exercise is just a small part of the average consumer’s day, and that it’s more useful to capture the bigger fitness picture.

For “high-resistance, low-movement exercises, none of these work really well, including us,” said Sonny Vu, chief executive of Misfit Wearables. But “it’s the other 23 and a half hours that’s the most interesting.”

Despite the occasional gaps, I found tracking to be useful if I focused less on the precise numbers and more on day-to-day variations in activity. Comparing the 16,000 steps I take on some weekend days to the 6,000 or 7,000 on a typical workday made me work harder to move more on weekdays.

Can trackers really change behavior in people? Last year, Dr. Rajani Larocca, a primary care physician at Massachusetts General Hospital, conducted a six-week lifestyle program for 10 patients with diabetes ages 50 to 70 that included weekly sessions to encourage exercise and healthful eating; each participant also was outfitted with a Fitbit Zip tracker.

“Every single person increased their activity,” Dr. Larocca said. “People felt more knowledgeable.” Eight months later, about half the patients from the group still wear a tracker.

Researchers at the Center for Connected Health in Boston have been giving activity trackers to subjects for six to nine months, then studying changes in their behavior. Dr. Kamal Jethwani, head of research at the center, said he saw three distinct groups of people among study participants.

About 10 percent are “quantified selfers” with an affinity for this kind of feedback; just by looking at the numbers, they are motivated to be more active. An additional 20 percent to 30 percent need some encouragement in addition to tracker data to effectively change their behavior.

But most of the subjects observed by Dr. Jethwani don’t understand the data and need help making sense of it. For them, he said, social motivation from a friend or joining a team or workplace challenge may be more effective.

I figure I’m in the second group, the ones who need a little push. One of my favorite features is the Jawbone UP’s inactivity alert. I set mine to vibrate on my wrist if I haven’t moved in the past hour. And Jawbone’s smartphone app offers personalized tips that are actually interesting. For instance: “When you go to bed 30 minutes later than average, you tend to take 971 fewer steps the next day.” And after several late nights, I was told: “Go to bed before 12:44 a.m.” Well, O.K.

Other trackers, like Fitbit’s, have tried to increase motivation by focusing on short-term goals — making it to 10,000 steps each day, for example. The Basis tracker awards points for keeping to “streaks” of healthy activity, like the number of days you’re active for more than 30 minutes.

Of the trackers I tested, Nike’s FuelBand put the strongest emphasis on competition with friends. But almost all the apps now have social features allowing you to share your activities, offer encouragement and hold one another accountable for goals.

All the data you’re recording is tied to a particular company’s software, so you can’t take it along if you decide to switch tracking devices. But many allow calorie data to be shared with other apps, like MyFitnessPal or LoseIt.

Having worn more of these trackers than any human should, I have to admit I am less captivated than I once was. Now I almost never look at the data that they collect.

But that’s not necessarily a bad thing.

“The goal should not be to make people wear the activity tracker for the whole year,” Dr. Jethwani said. “It’s to have them wear it when it’s meaningful” — that is, when better habits start to slip away.

These days, I’ve become keenly aware of how active I am and how active I need to be in order to feel healthy and energized. I don’t need a monitor anymore. I’m tracking me.